Window assemblies have historically been fabricated with a structural base frame and a sash frame, in addition to various trim pieces. The base frame is the portion of the window assembly which is attached to the structure of the building. The sash frame is the portion of the window assembly which holds the window pane and fits within the base frame. In some windows, the sash frame is fixed to the frame such that the window cannot be opened. In other embodiments, such as a casement window or a double hung window, the sash frame is movable with respect to the base frame.
Many materials have been utilized to construct window assemblies, such as wood, polyvinyl chloride (PVC), fiberglass and aluminum. Each of these materials has various advantages and disadvantages with respect to the other, such as cost, durability, aesthetics and the ability to prevent air and moisture infiltration. Frequently, the structural and trim pieces of a window assembly are constructed of the same type of material. However, it is sometimes the case that a window assembly will be constructed by using two different materials. For example, interior wood trim pieces have been used in conjunction with a vinyl window assembly to improve the interior aesthetics of the window assembly. Another example is where aluminum or vinyl exterior cladding has been added to a wooden window assembly in order to improve the durability of the window assembly without sacrificing interior aesthetics. In the prior art, including the above cited examples, the components of differing materials in the window assembly are often connected to each other through the use of separate mechanical fasteners and/or sealants. Improvements in window assemblies which utilize more than one material are desired.